Conventionally, lower olefins, such as propylene and ethylene, have been produced from oxygen-containing compounds, such as dimethyl ether and methanol, by dehydrating condensation reactions, in which zeolite catalysts are mainly used. Industrially, it has been desired to produce lower olefins from oxygen-containing compounds, such as dimethyl ether and methanol, economically with higher yield. More efficient processes and highly active catalysts have been required, and various studies have been conducted.
In order to improve the yield of lower olefins, reduction in feedstock partial pressure during reactions is conceivable. As such a method, for example, a technique has been known in which feedstocks are diluted with gas which is inert to reactions (Patent Document 1).
With respect to a technique for catalyst improvement, an alkaline-earth metal-containing MFI-type zeolite catalyst has been proposed as a catalyst giving a high yield of lower hydrocarbons synthesized from dimethyl ether and/or methanol, the alkaline-earth metal-containing MFI-type zeolite catalyst having a Si/Al atomic ratio of 30 to 400, an alkaline-earth metal/Al atomic ratio of 0.75 to 15, and an average particle size of 0.05 to 2 μm (Patent Document 2).
Furthermore, Patent Document 3 proposes a zeolite catalyst composed of a mixture including a proton-type zeolite or an ammonium-type zeolite which has MFI-type structure, an alkaline-earth metal compound, and a specific binder component. It is described that when the zeolite catalyst is used as a catalyst for producing lower hydrocarbons from dimethyl ether and/or methanol, aluminum is not easily detached from the zeolite framework, and the catalyst life is long.
Patent Document 5 proposes a zeolite catalyst shaped a mixture which contains pentacyl-type alminosilicate having a primary particle size of 0.01 to 0.1 μm. It is described that when the zeolite catalyst is used as a catalyst for producing lower olefins from methanol, the catalyst has high selectivity of lower olefins and good catalyst life.
However, an improved technique for producing lower olefins from an oxygen-containing compound more efficiently has been desired. Under these circumstances, the applicant of the present invention has conducted diligent studies, and as a result, has found that in the case where a catalyst is designed to have a specific form and the compacted bulk density (CBD) of the catalyst is specific range, surprisingly, a highly active catalyst can be obtained, a long catalyst life can be obtained even though the reaction conditions are under high temperature and pressure, the stable reactions can be achieved, and lower olefins can be produced efficiently. Thus, the present invention has been completed.
With respect to the technique for producing lower olefins from an oxygen-containing compound, the effect of the form, such as size and shape, of catalysts has not been verified. In catalytic cracking of hydrocarbons, such as hexane, it is described that, by using a zeolite catalyst having a large particle size of 1.2 mm or more, the pressure loss of a catalyst layer can be suppressed (Patent Document 4).